1. Field of the Invention
This invention relates to a switch adapted for use in a position sensor or the like of an automobile transmission and, more particularly, to a switch which is switched on or off by sliding a conductor plate resiliently supported to a holder between a fixed contact disposed on a substrate and the resin face of the substrate.
2. Description of the Prior Art
The conventional switch of this type is disclosed and known, for example, in U.S. Pat. No. 3,602,656.
FIGS. 11 to 14 show the switch disclosed in the above-mentioned U.S. Patent. FIG. 11 is a plan view of the switch; FIG. 12 is a bottom view of the holder of the switch; FIG. 13 is a sectional view of the holder of the switch; and FIG. 14 is a sectional view taken along the line 14--14 of FIG. 12.
In FIG. 11, reference numeral 1 denotes a substrate made of synthetic resin. A plurality of wiring patterns 2 forming fixed contacts made of a copper material are arranged on the surface of the substrate 1. Numeral 3 denotes a metal cover sealed to the substrate 1, and circular rotary openings 4 are formed at the cover 3 and the substrate 1. Numeral 5 denotes a holder made of synthetic resin. A cylinder 5a having an elliptical operation opening 6 at its center protrudes from one end of the holder 5, and the cylinder 5a is rotatably inserted into the rotary openings 4 of the substrate 1 and the cover 3.
As apparent from FIGS. 12 to 14, first and second conductor plates 7 and 8 are held on the rear surface of the holder 5, and the conductor plates 7 and 8 are opposed to the substrate 1. The first conductor plate 7 has a circular opening 7a at the lateral end of the holder 5, an engaging pawl 7b at the other end, two contacts 7c and 7d to bridge over the engaging pawl 7b at both longitudinal ends of the holder 5, and a spring retainer 7e at its center. The first conductor plate 7 thus formed is mounted on the holder 5 so that one end of the coiled spring 9 is wound at the spring retainer 7e, the circular opening 7a is engaged with the conical cylinder or projection 5a so that conductor plate 7 is rockably supported with the projection 5a as a fulcrum, and the engaging pawl 7b is contacted with a step 5b to prevent conductor plate 7 dropping from the holder 5.
The second conductor plate 8 has engaging pawls 8a and 8b at both lateral ends of the holder 5, two contacts 8c and 8d near the bases of the engaging pawls 8a and 8b, respectively, and further a spring retainer 8e at its center. The second conductor plate 8 is mounted at the holder 5 so that one end of the coiled spring 10 is wound at the spring retainer 8e, and both the engaging pawls 8a and 8b are contacted with steps 5e and 5f in grooves 5c and 5d formed at both lateral ends of the holder 5 to prevent conductor plate 8 dropping from the holder 5.
The switch thus constructed is carried in a vehicle to couple the operation opening 6 of the holder 5 to the coupling pin of a shift lever, not shown. Accordingly, when a driver moves the shift lever to a predetermined position, the holder 5 correspondingly rotates with the rotary opening 4 at its axis, and the contacts 7c, 7d and 8c, 8d of the first and second conductor plates 7 and 8 are separably contacted with the respective wiring patterns 2 to output desired position signals, such as position signals and/or back light signals, etc. In this case, both the contacts 7c and 7d of the first conductor plate 7 move in the extending direction of two parallel rows of the wiring patterns 2 as designated by two-dotted lines in FIG. 11. However, since the first conductor plate 7 is rockably supported to the projection 5a by means of the resilient strength of the coiled spring 9, even if there is a slight stepwise difference between both the wiring patterns 2 or between the substrate 1 and the wiring pattern 2, the conductor plate 7 can slide on the substrate 1 and the wiring pattern 2. Similarly, both the contacts 8c and 8d of the second conductor plate 8 move in the extending direction of the group of the innermost wiring patterns 2 in FIG. 11. However, since the second conductor plate 8 is elevationally movably held along the grooves 5c and 5d by means of the resilient strength of the coiled spring 10, even if there is a slight stepwise difference between the substrate 1 and the wiring pattern 2, conductor plate 8 can slide thereon.
The above-described plural rows of the wiring patterns 2 are not always brought into coincidence with the movable range of the holder 5. In such a case, the contacts 7c, 7d and 8c, 8d of the first and second conductor plates 7 and 8 are slid on the surfaces of the substrate 1 and the wiring pattern 2 upon rotation of the holder 5 irrespective of the on/off switching process. Wearing of the contacts 7c, 7d and 8c, 8d thereby causes the timing of the contacts between 7c, 7d, 8c, 8d and the wiring pattern 2 to become unstable. In other words, wear of the contacts 7c, 7d and 8c, 8d presents a serious drawback by causing a decrease in the on/off switching accuracy.
Since the contacts 7c, 7d and 8c, 8d of the first and second conductor plates 7 and 8 further slide on the metal wiring pattern 2, conductive wearing powder is generated. The metallic wearing powder can cause the shortcircuit between a plurality of fixed contacts of the wiring pattern 2. The nearer the fixed contacts approach the sliding direction of the conductor plates, the earlier the shortcircuit tends to occur. Thus, in such a case, it is necessary to provide a wearing powder reservoir between the fixed contacts.